Genetic Diversity environmental diversity enhances genetic diversity Levins (1968) predicted that environmental grain determines the level of polymorphism Finegrained species (highly mobile) would evolve a monomorphic strategy, whereas coarse-grained species (highly sedentary) would maintain polymorphism This theoretical prediction is largely supported by evidence (Nevo et al., 1984) The patterns and correlates of genetic diversity revealed in the global analysis for many unrelated species, subdivided into different abiotic and biotic regimes, strongly implicate selection in the genetic differentiation of species Natural selection in several forms, but most likely through the mechanisms of spatiotemporally varying environments at the various life cycle stages of organisms, appears to be an important evolutionary force causing change at the molecular level Other evolutionary forces, including mutation, migration, and genetic drift, certainly interact with natural selection, either directly or indirectly, and thereby contribute differentially, according to circumstances, to population genetic differentiation at the molecular level However, the final orientation of the evolutionary process is determined by natural selection (Bell, 1997) 669 Regional Analysis of Genetic Polymorphisms Regional: Allozyme Diversity across Phylogeny in Israel and the Near East Israel as an Ecological Genetic Laboratory of Increasing Aridity Southwards Our regional analyses of genetic diversity extended over Israel and the Near East We used Israel, with its remarkable physical and biotic diversities, as a medium to large-scale ecological genetic laboratory (Nevo, 1988, 1998) In 1988, Nevo and Beiles conducted an ecological test of protein polymorphism in 13 unrelated taxa of plants, invertebrates, and vertebrates involving 21 species, 142 populations, and 5474 individuals (Figure 3), following the extensive studies of allozyme diversity in 38 species in Israel Each individual, population, and species were tested, on average, for 27 enzymatic gene loci These species varied in population size and structure, life histories, and biogeographical origins, but they largely shared geographically short and ecologically stressful gradients of increasing aridity in Israel, both eastward (70 km) toward the Syrian and Jordanian deserts and (mainly) southward (260 km) towards the Negev desert We found genetic parallelism across most taxa Theba pisana 0.2200 0.1925 He Dociostaurus ourvioercus 0.1650 Bufo viridis 0.1375 Sphincterochila Gryllotalpa gryllotalpa 0.1100 Average across taxa Hordeum spontaneum 0.0625 Rana ridibunda Hyla arborea Agama stellio 0.0550 Gerbillus allenbyl Triticum dicoccoides Spalax ehrenbergi Acomys cahirinus 0.0275 0.24 0.25 0.26 0.27 0.28 0.29 0.30 0.31 0.32 0.33 0.34 0.35 0.36 0.37 0.38 0.39 0.40 Rainfall variation Figure Parallel genetic patterns in the level of gene diversity, He, of 13 enzymatic systems averaged across all taxa studied here The average regression line is He ẳ 0.0556 ỵ 0.4803 RV The only change is that Gryllotalpa gryllotalpa has been divided into two species, G tali (2n ¼ 19) and G marismortui (2n ¼ 23) See Broza et al., 1998, cited in Nevo, 1999 The regression line represents G tali (reproduced from Nevo E and Beiles A (1988) Genetic parallelism of protein polymorphism in nature: Ecological test of the neutral theory of molecular evolution Biol J Linn Soc 35: 229–245)